As before, the principle aim is to characterize and quantify the hormonal and substrate controls in man and experimental animals which regulate the deposition and mobilization of various stored fuels. Fasting man and man fed simple meals are the main models. Particular emphasis will be placed on the role of the red cell in amino acid transport, since it has recently been found that it plays an active role in the transfer of nitrogen from one tissue to another. In vitro experiments using the isolated hind limb preparation will be used for further physiologic clarification.